Light and Plastid Signals Regulate Different Sets of Genes in the Albino Mutant Pap7-1

Abstract

Plants possessing dysfunctional plastids due to defects in pigment biosynthesis or translation are known to repress photosynthesisassociated nuclear genes via retrograde signals from the disturbed organelles toward the nucleus. These signals are thought to be essential for proper biogenesis and function of the plastid. Mutants lacking plastid-encoded RNA polymerase-associated proteins (PAPs) display a genetic arrest in eoplast-chloroplast transition leading to an albino phenotype in the light. Retrograde signaling in these mutants, therefore, could be expected to be similar as under conditions inducing plastid dysfunction. To answer this question, we performed plastome-and genomewide array analyses in the pap7-1 mutant of Arabidopsis (Arabidopsis thaliana). In parallel, we determined the potential overlap with light-regulated expression networks. To this end, we performed a comparative expression profiling approach using light-and dark-grown wild-type plants as relative control for the expression profiles obtained from lightgrown pap7-1 mutants. Our data indicate a specific impact of retrograde signals on metabolism-related genes in pap7-1 mutants reflecting the starvation situation of the albino seedlings. In contrast, light regulation of PhANGs and other nuclear gene groups appears to be fully functional in this mutant, indicating that a block in chloroplast biogenesis per se does not repress expression of them as suggested by earlier studies. Only genes for light harvesting complex proteins displayed a significant repression indicating an exclusive retrograde impact on this gene family. Our results indicate that chloroplasts and arrested plastids each emit specific signals that control different target gene modules both in positive and negative manner.

Cytokinin-Regulated Expression of Arabidopsis thaliana PAP Genes and Its Implication for the Expression of Chloroplast-Encoded Genes

“…In accordance with this premise, in both mutant lines tested, the expression levels of class I genes psaB, psbD , and rbcL were drastically reduced and were not significantly affected by CK, similarly to the expression pattern of nuclear-encoded LHCB2.4 (light harvesting antenna protein of PSII) whose gene product is targeted to chloroplasts ( Figure 6 B). On the contrary, mRNA levels of class III genes which are enhanced in pap mutants [ 10 , 19 , 20 , 29 ] were either down-regulated ( rpoA, rpoB ) or did not respond to CK treatment ( accD ). The expression of class II gene atpB remained unaltered or slightly induced in the mutants and wild-type plants while that of clpP was up-regulated.…”

“…PEP is mainly responsible for transcription of photosynthesis genes. It exists in two forms: PEP-B composed of 4-plastid encoded core subunits (α, β, β’ and β’’) and a sigma factor and PEP-A where core subunits of multimeric PEP became decorated with at least 12 additional nuclear encoded proteins [ 9 , 10 ]. PEP-B is responsible for the activity in etioplasts and at the early stage of greening, while PEP-A becomes active during light-dependent chloroplast development [ 11 ].…”

Retrograde signals from mitochondria reprogramme skoto-morphogenesis in Arabidopsis thaliana via alternative oxidase 1a

“…Analysis of microarray data was performed as indicated in [26]. The cel files containing the scanned chips received from KFB were analyzed with RobiNA [27] with the background correction method RMA (robust multi-array average expression measure) [28], p-value correction method Benjamini-Hochberg [29] and the analysis Strategy Limma for the quality control [30].…”

Protein lysine methylation contributes to modulating the response of sensitive and tolerant Arabidopsis species to cadmium stress

“…We obtained homozygous T‐DNA insertion lines disrupting 23 of the selected genes (Table S1). Three genes could not be retained for the screening, of which PAP7 for which the mutation is lethal in photoautotrophic conditions (Grubler et al, ).…”